Browsing by Subject "Energy balance model"
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Item Debris-covered glaciers : modeling ablation and flood hazards in the Nepal Himalaya(2016-05) Rounce, David Robert; McKinney, Daene C.; Maidment, David R; Hodges, Ben R; Catania, Ginny A; Yang, Zong-LiangDebris-covered are ubiquitous in the Nepal Himalaya and significantly alter the glaciers response to climate change and have large implications on the development of glacial lakes. The thickness of the debris is largely heterogeneous over the course of the glacier thereby promoting ablation in areas of thin debris and retarding ablation in areas of thick debris. The debris thickness typically increases towards the snout of the glacier, but can be difficult to measure as field measurements are time-consuming and laborious. This body of work utilizes satellite imagery in conjunction with a debris-covered glacier energy balance model to reasonably estimate the spatial variations in debris thickness for glaciers in the Everest region of Nepal. Sub-debris ablation rates may be computed using the same energy balance model, but requires detailed information regarding the properties of the debris and the surface processes. Detailed field data was collected over the 2014 melt season on Imja-Lhotse Shar Glacier to estimate many of the debris properties. This data was also used to model the sub-debris ablation rates to develop an understanding of the critical properties (i.e., thermal conductivity, albedo, and surface roughness) and processes (i.e., accounting for the latent heat flux) required to accurately model the impact of the debris. The heterogeneous debris cover often causes higher melt rates upglacier, which diminishes the glacier’s topographic gradient thereby promoting glacier stagnation and the development of glacial lakes. These glacial lakes form behind terminal moraines comprising soil and loose boulders that are susceptible to fail causing a glacial lake outburst flood (GLOF). GLOFs can have devastating impacts on infrastructure and communities located downstream; however, assessing the risks associated with these floods has traditionally required detailed field campaigns that are difficult to perform as these glacial lakes are located in remote areas at high altitudes. This body of work develops a holistic hazard assessment using solely remotely sensed data to objectively characterize the threat of a GLOF. This hazard assessment provides valuable information concerning potential GLOF triggers that may be used to direct future field campaigns and ultimately the management actions associated with these glacial lakes.Item Occurrence and Stability of Glaciations in Geologic Time(2011-10-21) Zhuang, KelinEarth is characterized by episodes of glaciations and periods of minimal or no ice through geologic time. Using the linear energy balance model (EBM), nonlinear EBM with empirical ice sheet schemes, the general circulation model coupled with an ice sheet model, this study investigates the occurrence and stability of glaciations in geologic time. The simulations since the last glacial maximum (LGM) suggest that the summertime thawline of ice sheets conforms closely to the equatorward edge of the ice sheets and implies the relative stability toward deglaciation. CO2 levels are indispensable in controlling the initiation of ice sheet in the Cretaceous. At low CO2 levels, ice sheets exist in all periods no matter LGM or the last interglacial (LIG) orbital elements; however, at high CO2 levels ice sheets rarely exist. The simulations agree well with recent geological evidence of the hysteresis of glaciations in the Permo-Carboniferous. Gondwanaland reached its glacial maximum when CO2 level was roughly the same or slightly higher than the preindustrial value. With a further increase of CO2, deglaciation dominates and results in an ice free state. Again, if CO2 decreased to the present level, Gondwanaland would be glaciated once more and start a new cycle of glaciation and deglaciation. Simulations from five paleogeography maps in Gondwanaland with a suite of CO2 levels and different orbital elements reveal that paleogeography, CO2 levels and the Milankovitch cycles all contribute to the glaciations of Gondwanaland. This study shows that orbital elements alone are insufficient to account for the evolution of ice sheets. Net radiative forcing caused by greenhouse gases, such as CO2 and solar constant change are the primary drivers to glacial inception or demise. Continental geography, CO2 levels, solar constant change, and the Milankovitch cycles complicate the glacial history of Earth.